Polycarbonate resins are transparent, transmit light and are used in a broad range of applications in electrical, electronic, OA, automotive and other areas.
When a polycarbonate resin is used in applications such as direct lighting and edge lighting type units for liquid crystal televisions, lighting device covers, switches in various devices and the like, the light source is visible when the resin transmits light. Therefore, a material having sufficient light diffusing properties such that it does not reveal the shape of the light source (a lamp) behind a molded resin product without adversely affecting the luminance of the light source as much as possible is being sought.
In the conventional technology, a method was used in which polymer or inorganic particles with a different index of refraction were added as a dispersed phase to a thermoplastic resin forming a continuous phase for the purpose of imparting light diffusing properties to the polycarbonate resin. In addition, methods to realize desired light diffusion properties by adjusting the refractive index difference between the dispersed phase and the continuous phase or the size of the particles in the dispersed phase have been proposed. (References 1 and 2)
Similarly a light storing agent that emits light for an extended period of time when the irradiation is completed after an optical excitation, for example, using ultraviolet rays, is used in night time display applications such as evacuation markers and display lights and the like. (References 3 and 4)
Furthermore, a diffusion sheet with an even higher degree of optical performance could be obtained by using a light diffusing agent and a light storing agent in a clear thermoplastic resin such as a polycarbonate resin. (Japanese Patent Application No. 2005-165178)    Reference 1: Japanese Patent Application Public Disclosure (Kokai) No. S60-184559    Reference 2: Japanese Patent Application Public Disclosure (Kokai) No. H03-143950    Reference 3: Japanese Patent Application Public Disclosure (Kokai) No. H07-240187    Reference 4: Japanese Patent Application Public Disclosure (Kokai) No. 2000-156107
Although polycarbonate resin is a highly flame retardant plastic material possessing self extinguishing properties, even better flame retardance is being sought in order to satisfy the need for safety in electrical, electronic and OA applications where light diffusing sheets are used.
A method in which a large amount of an oligomer or a polymer of the carbonate derivative of brominated bisphenol A has previously been used to improve the flame retardance of polycarbonate resins.
However, the addition of a large amount of halogenated compound containing bromine raised a concern about the generation of a gas containing the halogen. In addition, the use of a flame retarding agent that does not contain chlorine, bromine and the like is desired from an environmental perspective.